Recently the demand of motors has greatly increased in various fields such as the automobile industry, the aerospace industry, the armament industry, medical devices, and home appliances. Additionally, an upsurge in the price of rare-earth resources causes an increase in the per-unit cost of motors that have permanent magnets of rare-earth resources in a rotor.
As one of alternatives to obviate the above problem, a switched reluctance motor attracts attention in these days. A switched reluctance motor rotates a rotor by using a reluctance torque generated according to variations in magnetic reluctance.
Normally, in a conventional switched reluctance motor, each of a stator and a rotor has a salient structure. The stator has coils wound on salient parts thereof to generate a reluctance torque according to variations in magnetic reluctance, and the rotor has no magnetization mechanism such as a coil or a permanent magnet. The rotor is connected, at a central part thereof, to and rotated together with a rotational axis that transmits a driving force of the motor.
Such a conventional switched reluctance motor rotates the rotor, depending on only a reluctance torque generated from the coils wound on the stator salient parts. Therefore, the conventional switched reluctance motor may have a lower output than that of a motor in which a rotor includes any magnetization mechanism.
In order to solve this problem, a way of adding permanent magnets to the stator may be considered. However, due to a magnetic flux produced at the stator salient parts on which the coils are wound, a stator core part of the conventional switched reluctance motor may have a portion where the reversal of a magnetic flux occurs and the other portion without the reversal of a magnetic flux. Therefore, if permanent magnets are added to the stator to enhance the output of the switched reluctance motor, a magnetic flux generated from the permanent magnets may offset a magnetic flux generated from the coils in a portion where the reversal of a magnetic flux occurs. Unfortunately, this may invite a reduction in a magnetic flux of the coils.